Sakuro's Disease

Sakuro's Disease was a very rare, life-threatening illness. According to Leonard McCoy, in 2267, the chances of contracting it were literally billions to one. It was caused by a pathogen of some sort. The disease was detectable long before it was symptomatic. Symptoms included fever, emotional lability, and coma leading to death. The disease was always fatal if untreated, but as of the 23rd century, it could be cured at a hospital.